If the box is 1/2" back you already have a violation but let's put it 1/8" back and you still don't have it made up tight to the box. I assume the thinking is the screw is bonded to the yoke with the spring clip and a couple threads worth of contact with the box ear bonds the screw to the box. I agree with you, it stinks. That will probably operate the breaker in a fault condition but I would not count on it giving you a noise free ground for your electronics and it will probably arc a bit before it welds and becomes a bolted fault.
406.4(A) says that the receptacle "shall be installed such that the mounting yoke or strap of the receptacle is held rigidly at the finished surface."
If the receptacle is held by the 6-32s so it's tight against the sheetrock and doesn't move around, it satisfies 406.4(A), even if the receptacle isn't tight against the box. And if it's the self-grounding type, it seems like it'd be effectively grounded according to 250.146(B).
However, 314.20 says that you still need a spacer if the box is set back farther than 1/4" from the finished wall surface.
All that said when I did maintenance work 95% of my receptacle repairs were because the box was set back from the sheetrock and there was no spacer for the receptacle. Eventually the sheetrock would crumble because of the force of people pushing plugs into the receptacles, and then the receptacle wouldn't be mounted to anything.
i agree with big john, just wanted to add: if thae wall is wood,then your box cannot be set back- it shound be flush. and- if you have that problem with the drywall crumbling,the box will need "mudded around so there isn't more than an 1/8" gap around the perimeter of the device ring per 314.21. also --"caddy" makes a metal piece that looks similar to a madison strap,it goes on when installing the plug. the ears on the plug rest against the metal which has a surface area just slightly smaller than the cover plate. it helps prevent the crumbling problem.
The device is listed as grounded (and I mean both switches and receptacles) solely by means of the screw contact. It does not have to be in contact with the mudring to comply with the listing. (come on what percentage of devivces actually contact the mudring?...2%....3%? )_
Even when you use 5/8" rings with 1/2" drywall and 3/4" rings with 5/8" drywall the sheetrock installers rarely manage to suck the rock up enough to overcome the protrudeing box screws that hold the rock out a good 1/8"......
Most electricians are scared to even try useing "overdepth" rings for the drywall like I routinely do. Why?...because drywallers are a crapshoot and even when they are doing a great job there will still be a wide variation in how deep your boxes are given modern methods. (zip tools) A mudring that is recessed too far is easier to ignore than one that protudes even by an 1/8th of an inch.....sigh....
Add to that saving money buy not buying bracket boxes and secureing them with all four screw holes.......nope...screwing four-squares directly to the studs with two 45 degreed screws...or the use a spring metal clip in the areas that will still accept such methods is the method of choice....with a usually unavoidable and by code unacceptable increase in mounting depth from the stud face.....
Sigh....stack some washers on the 6/32's or as we have done since way before I got into the trade 25+ years ago wrap some bare 12 around the screws so the receptacle has a solid surface to support it and the plate doesn't split when you force a plug into it.
But anyway I'm ranting off topic....yes the receptacles and switches are listed as grounding....no they don't have to contact the mudring to achieve that rating.
We have a deal that the rockers are to observe, and MUST pay attention to the location of any outlets. As I've mentioned before on a couple of forums here, we charge the GC or the HO $1000.00 per covered outlet or $10,000.00 per half day to come back and "uncover" the hidden outlets.
We have had to charge it a couple of times now and it works quite effectively. It's all contained and explained beforehand during the signing of the contract during the acceptance interview. Extra effort is placed during the interview to make sure that the exact details are clearly and usually painfully, slowly and in overbearing detail, leave the customer zero doubt in their mind as to what will actually be done.
We make sure and at least triple check the stud mounting to make absolutely sure that the outlets are at the specific depth for the drywall that's going to be installed. I'll settle for nothing less and I've been called more than a few bad worded names by a GC or HO for holding up a rocker for a couple of minutes so he can do his job in a proper fashion too.
I've found out that some boss rockers don't give an iota pinch of coon sh@t about the electrical, plumbing, air handling//or any other trade, as long as they can get everything "covered" up as soon as possible and then leave.
If it buggers up our work, that contractor soon passes along our invoice for either $1G or 10G's or maybe more to the rockers Company. From there - I have no idea where it goes, except to say that lately we have not had to deal with this issue much.
Right before my wife was "downsized" she took a warranty call in another neighborhood for a bow in a wall and it was a buried receptacle that nobody (or everybody, depending on how you look at it) missed. They did a little careful measuring, poked a little hole that hit the box, cleaned up the hole and kicked the drywall tight to the studs. patch and paint, off you go.